Alternative pretreatments for gold-bearing refractory stibnite

The aim of this work was to compare a chemical and a biological process as a pretreatment for gold recovery from a refractory gold-bearing stibnite. Experimental tests have been conducted at laboratory scale, utilising an ore sample with gold content of about 20 g/t Au, coming from South America. The chemical pretreatment consisted in alkaline leaching by aqueous sodium sulfide and sodium hydroxide solutions; after chemical leaching, metallic antimony was selectively recovered by electrowinning. The biochemical pretreatment has been carried out in acid environment by bacterial cultures of Thiobacillus genus. The optimisation of the parameters permitted to attain an increasing on gold recovery from 20% Au (not pretreated samples) to about 80% Au, in both processes. Two integrated process flow-sheets have been outlined.